Trickle valves, also called flap valves or the like, for such purpose are known from e.g. U.S. Pat. No. 4,494,564 or U.S. Pat. No. 5,740,834. The valve is provided at the bottom exit of a separating cyclone in a plant handling particulate material. The trickle valve is provided in the downwardly extending conduit from the bottom outlet of a separating cyclone. The material is then fed into a conduit or the like for further treatment. In such plants the pressure in the conduit downstream the valve is higher than the pressure in the cyclone so in order to prevent rising air from entering into the cyclone the trickle valve is installed. The trickle valve is a one-way valve allowing the separated particulate material from the cyclone to be fed from the cyclone whilst preventing air from flowing in the opposite direction due to a building up of a material plug in the upper part of the trickle valve. In operation, a steady flow of particulate material will leave the trickle valve as long as it is continuously fed with material. The flow rate is determined by the amount of material supplied from the cyclone.
In some applications for instance in the field of making mineral fibres from melting of particulate mineral material, the known trickle valve assemblies are not suitable as the trickle valve outlet conduit directly upstream of the valve tends to block due to clogging of material, i.e. the material makes a compact plug and does not flow freely from the trickle valve. A characteristic of this application is that the conduit has a relatively small diameter combined with relatively coarse material forming a relatively high material plug. Trickle valves are normally used in plants with a large outlet diameter (e.g. 1 m) combined with small material size (e.g. 50-100 μm).
On this background it is an object of the present invention to provide a valve assembly of the trickle valve type which ensures a steady material flow through the valve and prevents clogging due to the dimensions of the conduit, height of material plug and particle size of the material.